Perching. All passerines have four toes on each foot. Three of the toes point forwards. The other toe points backwards. This means that passerines can easily hold onto trees or rocks. Because of this, they are also known as perching birds. A tendon in the rear of the leg makes the foot curl and grip when the bird lands on a branch. This is more than just a convenience for the birds: it is a locking mechanism so they can sleep without falling off.[2]

All passerine chicks (babies) are born in an undeveloped state: they need parental help.[3] Their eyes are closed, and they are bald, with little or no down. They cannot leave the nest, and must be fed by the parents. The advantage of this is that their brains grow larger during the fledgling stage. In birds which leave the nest early, their brains depend mainly on material in the egg. Passerines have significantly large brains compared to body size, and many passerines are comparatively intelligent.[4]

All passerines have 12 tail feathers. This is a basaltrait, a feature inherited from their past. It leads biologists to think this large group originally had one common ancestor.

The early fossil record is poor because the first Passeriformes were on the small side, and their delicate bones did not preserve well. Two specimens from Queensland, Australia are fossil bone fragments clearly recognizable as passeriform. They are two species of about 10 and 20 cm in overall length. This proves that some 55 mya, barely into the early Eocene, early perching birds were recognizably distinct.[7] It also suggests that the origin of this great order of birds was in the southern continent.

There are three sub-orders: Acanthisitti, Tyranni and Passeri. There are only two bird species in the sub-order Acanthisitti. They are known as New Zealand wrens. The sub-order Tyranni are also known as the suboscines. Many of these birds are found in tropical areas. The sub-order Passeri has the most bird species. They are also known as the oscines. They have the best songs of all birds.

Golden-headed manakin (Pipra erythrocephala)

Rainbow pitta (Pitta iris), a dark bird with bright color patches. Most Pittidae have similar colors

Superfamily Corvida – a highly diverse group of global distribution, but most plentiful in the Australasian region and surroundings. The oldest truly globally successful group of passerines, they include among them what may well be the most intelligent and the most spectacular of the order.

Superfamily Sylvioidea – mostly insectivores, distribution centered on the Indo-Pacific region. Few occur in the Australian region and fewer still in the Americas. Usually sleek and drab birds, few have pronounced sexual dimorphism.

Superfamily Muscicapoidea – mostly insectivores, near-global distribution centered on Old World tropics. One family endemic to Americas. Nearly absent (except introductions) from the Australian region. Usually rather stocky for their size, most are quite dark and dull though Sturnidae are commonly iridescent and/or colorful. Sexual dimorphism often absent, sometimes pronounced.

Superfamily Passeroidea – mostly herbivores including many seed-eaters, near-global distribution centered on Palearctic and Americas. Includes the Nine-primaried oscines (probably a subclade). A very high proportion of colorful and highly sexually dimorphic forms.